It is well known that interference spectrometers offer significant advantages compared to conventional grating spectrometers in the study of faint, extended sources. The primary advantages are (1) an etendue (or throughput) which is typically 200 times larger than grating spectrometers operating at similar resolutions, (2) compact size, especially at high spectral resolution, (3) no requirement for high precision optics in the input/output optical systems, and (4) relative ease of obtaining high spectral resolution. In combination, these advantages offer important economies in observation time, cost, weight and volume for many important programs, particularly where size and weight are crucial as in satellite based systems.
All reflection, scanning Fourier transform spectrometers utilizing these principles are presently available and have been thoroughly studied. See, e.g., R. A. Kruger, L. W. Anderson, and F. L. Roesler, "All-Reflection Interferometer for Use as a Fourier Transform Spectrometer," J. Opt. Soc. Am., Vol. 62, 1972, p. 938 et seq; F. L. Roesler, "Fabry-Perot Instrument for Astronomy," in Methods of Experimental Physics, Vol. 12, Part A: Optical and Infrared, Academic Press, New York, 1974; R. J. Fonck, et al., "All Reflection Michelson Interferometer: Analysis and Test for Far IR Fourier Spectroscopy," Applied Optics, Vol. 17, 1978, p. 1739 et seq. Such scanning instruments have the advantages of interference spectroscopy, but require complex driving and control mechanisms for the scanning components, e.g., the moving mirror, which are complicated, expensive, and subject to maintenance and reliability problems inherent in an instrument employing moving parts.